The present invention relates to a curling apparatus for curling the end of a tapered cylinder made of sheet metal.
A conventional method of curling the end of a tapered cylinder is explained with reference to FIG. 11 through FIG. 13, in which FIG. 11 and FIG. 12 are enlarged sectional drawings showing the relationship between a workpiece and a conventional curling apparatus.
In FIG. 11, a roll base consists of a roll 1 for spinning work, along the outer peripheral of which a V-groove is formed with the bottom surface shaped through a circular arc, a radial bearing 2 being fastened to the surface of an inside diameter, a supporting shaft 4 to support the roll 1 universally rotatable together with thrust bearings 3 disposed on both ends, and a supporting stand 7 which is disposed radially on a periphery of a swiveling table 6 and which is fastened to the supporting shaft 4 with a key 5.
A tapered cylinder 8 made of steel metal for curling work is formed in advance with a pre-curved area 8a on a curling side of the lower end.
The conventional curling apparatus is arranged with more than 3 roll tables which are radially arranged at equal intervals and is disposed concentrically on a power-driven swiveling table 6, and is provided with a pressure device (not illustrated here) for pushing down a tapered cylinder 8 on an upper part. Explanation follows of the operation of the curling apparatus thus structured. As shown in FIG. 11, by mounting a preformed tapered cylinder 8 on the roll 1 situated on the roll table, push the tapered cylinder 8 is pushed with the pressure apparatus against the roll 1 by rotating swiveling table 6. The roll 1 rotates universally on the supporting shaft 4 against a friction force with the tapered cylinder 8, and as shown in FIG. 12, the V-groove 1a serves as a guide to roll the periphery of the lower end of the tapered cylinder 8 to the inside.
However, with the structure as mentioned above, the radial position of the roll 1 so fastened with the thrust bearing 3 prevents the formation of a desirable, complete tapered surface. Instead, as shown in FIG. 13, a bulge 8a is generated in the neighborhood of the lower end of the tapered cylinder 8 due to a radial component generated when it is guided by an outer wall of the V-groove 1a as shown with an arrow B.